Conventionally, for coupling a photonic integrated circuit to an optical signal originating, for example, from an optical fiber, an optical coupler is implemented in the active layer of the integrated circuit for redirecting the light signal into a waveguide implemented in the structure.
During coupling, one part of the input optical signal passes through the coupler and is not transmitted in the waveguide. Means exist for improving the efficiency of the coupling, such as optimizing the thickness of the buried insulating layer in the case of a Silicon-On-Insulator (SOI according to the abbreviation well known to the person skilled in the art) substrate. However, even with an optimum thickness, a part of the signal is lost.
Another solution consists in placing a reflective layer, for example, a metal layer, under the buried layer, in order that the rays passing through the coupler are reflected and pass back again into the coupler. However, the production of such a metal layer requires specific method steps.